1. Occurrence and Significance
Strontium (Sr) is the fourth element in Group IIA of the periodic table. It has an atomic number of 38, an atomic weight of 87.62, and a valence of 2. The average abundance of Sr in the earth’s crust is 384 ppm; in soils Sr ranges from 3.6 to 160 ppm; in streams it averages 50 μg/L, and in groundwaters it ranges from 0.01 to 10 mg/L. Strontium is found chiefly in celestite (SrSO4) and in strontianite (SrCO3). Strontium compounds are used in pigments, pyrotechnics, ceramics, and flares. 90Sr is a fission product of nuclear reactor fuels and was widely distributed on the earth’s surface as a result of fallout from nuclear weapons testing.
The common aqueous species is Sr2+. The solubility of strontium is controlled by carbonate and sulfate. Some compounds are toxic by ingestion and inhalation. Although there is no U.S. EPA drinking water standard MCL for concentration of strontium, strontium-90 measurements are required when the gross beta activity of a water sample is greater than 50 pCi/L. The U.S. EPA primary drinking water standard MCL for 90Sr is 8 pCi/L.
A method for determination of 90Sr is found in Section 7500-Sr.